2021MNRAS.506L..45Z

We report the discovery of a very dense jet-like fast molecular outflow surrounded by a wide-angle wind in a massive young stellar object (MYSO) G18.88MME (stellar mass ∼8 M_☉) powering an extended green object G18.89-0.47. Four cores MM1-4 are identified in the Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum map (resolution ∼0.8 arcsec) towards G18.88MME, and are seen at the centre of the emission structure (extent ∼0.3 pc x 0.2 pc) detected in the ALMA map. G18.88MME is embedded in the core MM1 (mass ∼13-18 M_☉), where no radio continuum emission is detected. The molecular outflow centred at MM1 is investigated in the SiO(5-4), HC₃N(24-23) and ¹³CO(2-1) lines. The detection of HC₃N in the outflow is rare in MYSOs and indicates its very high density. The position-velocity diagrams display a fast narrow outflow (extent ∼28 000 AU) and a slower wide-angle more extended outflow towards MM1, and both of these components show a transverse velocity gradient indicative of a possible rotation. All these observed features together make G18.88MME as a unique object for studying the unification of the jet-driven and wind-driven scenarios of molecular outflows in MYSOs.